Semester

Fall

Date of Graduation

2000

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mining Engineering

Committee Chair

W. Peng

Committee Co-Chair

W. Khair

Committee Member

Y. Luo

Abstract

Weightings are dynamic phenomenon observed in mines where coal is extracted using the longwall mining method. Weightings are characterized by high convergence rates within the powered supports which maintain roof stability along the longwall face. Rapid convergence is induced by ground pressures that exceed the load capacity of the supports, and forces them to yield. A weighting event need not necessarily impact the mining process negatively, but notable cases exist where weightings have caused extensive damage to roof strata resulting in large roof falls and prolonged periods of lost coal production.;This thesis describes the history of four longwall panels (No's 5 East, 6 East, 7 East, 8 East and 3 Center) at Phalen Colliery, where weightings (occurring at periodic intervals) resulted in eight (8) major roof falls. The largest of these weighting events halted longwall production for seven (7) months. The roof falls were eventually rehabilitated by filling the resulting fall cavities with foam cement. The cost of recovery was expensive (in excess of {dollar}15,000,000), and resulted in {dollar}100,000,000 of lost coal sales.;A geotechnical examination of the weightings revealed a close relationship to the presence of a strong, thick sandstone bed in the immediate roof strata and remnant coal pillars in overlying abandoned Harbour Seam workings. Observation of roof support hydraulic pressures using the INSITE(TM) monitoring system clearly identified several of the weightings and their periodic nature. Significant water inflows from the roof (at the face) during many of the weightings, proved to be an effective tool for mapping their location.;Longwall weightings cannot be avoided when the physical environment is conducive to their creation. The risk of experiencing roof falls associated with the weightings however, can be dramatically reduced by operating the longwall in an efficient manner. Longwall mining experience at Phalen Colliery has shown that operational factors most influential in attenuating the roof fall hazard include: the availability of high capacity, well maintained hydraulic roof supports; a workforce that has been thoroughly trained in the proper operation and maintenance of all face equipment; a comprehensive geotechnical monitoring program, and management systems that help provide a continuous interchange of information among face workers, supervisory personnel, engineering staff, and maintenance support crews. A concerted effort to keep the longwall face operating continually is considered crucial for alleviating the roof fall hazard associated with longwall weightings.

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